Field of the Invention
The present application relates to a coating method.
The present application further relates to a coating apparatus.
Related Art
Many products, such as food products, electronic components and the like, require an enclosure that protects them from influences by moisture, oxygen, hydrogen and/or other substances. Barrier layers comprising alternating organic and inorganic layers have been proven suitable as an enclosure. The material in the inorganic layers provides the highest barrier against said substances, but these layers usually have defects via which these substances may still leak. An organic layer decouples mutually subsequent inorganic layers so that the substances may only penetrate via a tortuous path, which inhibits diffusion.
U.S. Pat. No. 5,725,909 describes an apparatus and a method for coating a sheet substrate with acrylate and oxygen barrier layers in a continuous process. In the apparatus described therein with reference to FIG. 4, the sheet is guided along a rotatable drum. While being guided around the drum an acrylate layer is deposited at the sheet by a flash evaporator, and polymerized by an UV source. A further deposition station deposits a barrier material e.g. by plasma deposition, vacuum deposition or the like. This is followed by a further evaporator that deposits a further acrylate layer that is subsequently polymerized.
It is a disadvantage of the known apparatus and method that it is only possible to apply relatively thin organic layers, e.g. of less than a micrometer. Also, in order to be capable to apply UV-curing to the acrylate layer, this layer should in addition to an acrylate monomer or other precursor comprise a photo-initiator. These components should be simultaneously evaporated, which implies the requirement that they have a comparable vapor pressure. Relatively thick organic layers are desired as they can better cover irregularities in the inorganic layers. Moreover a relatively thick organic layer e.g. thicker than about 10 μm is very suitable to embed functional particles, such as getter materials and optically active particles such as microlenses or scattering particles.
U.S. Pat. No. 5,725,909 also mentions spraying as a method to apply a thicker acrylate layer, e.g. of 25 μm. However, when replacing the flash evaporator of FIG. 4, by spraying nozzles, the sprayed substances will also distribute in the atmosphere of the vacuum chamber, so that the conditions for deposition of the oxygen barrier material are no longer met.